During the last few decades, liposomes (also known as bilayer lipid vesicles) are increasingly being used to encapsulate and deliver pharmaceutical compounds. Liposomes comprise one or more lipid (such as phospholipid), bilayers and can contain other molecules, such as proteins or carbohydrates, in their structure. The lipidic layer on the liposome confines and protects the enclosed pharmaceutical compound until the liposome reaches its destination and adheres to the outer membrane of targeted cells. By this process, drug toxicity to healthy cells is minimized and therapeutic efficacy can be increased. Due to the presence of both lipid and aqueous phases in their structure, liposomes can be utilized in the encapsulation or entrapment of water- and lipid-soluble material in addition to amphiphilic compounds.
Liposomes can be used in vaccine/immunogenic compositions in the formulation of adjuvant compositions. As these adjuvant compositions are often parenterally administered to humans, it is desirable that these are sterile. Liposomes used as adjuvants are generally submicron liposomes and are sufficiently small to be sterile-filtered through 0.2 μm filters. It is an object of the present invention to provide a process for improved filtration of submicron liposomes.